Field of the Invention and Related Arts
This invention relates to an extinction type detector for detecting a concentration or density of a gas or vapor within a space on the basis of an attenuation of light due to the gas or vapor present within the space.
In a conventional extinction type detector, a light emitting device and a photodetector device are disposed oppositely, keeping a space of 1m or so therebetween, so that a change in an amount of received light, which is causable by a gas or vapor intervening between the devices, such as a combustion gas, smoke, etc. caused, for example, by a fire.
However, such a conventional extinction type detector has a disadvantage that it requires a long detecting space as described above, rendering the detector bulky.
To solve this problem, there has been proposed a detector which utilizes reflecting mirrors for effecting multiple reflection so as to obtain a desired effect with a detecting distance reduced between the devices.
However, this proposed detector is complicated in structure and can not be small-sized as desired.
Further the devices commonly used as light emitting elements are, in general, liable to decrease their light emission due to deterioration with age or temperature fluctuation. If such a change in the performance is once caused, an output may be produced due to the deterioration of the elements even when gases or vapors of the same density or concentration come in. Thus, accurate detection can hardly be expected. More particularly, since the concentration or density is determined on the assumption that the value of the output is proportional to the concentration or density. Therefore, if the conditions of the light emitting element are changed and the light emission amount is reduced, decreasing the output value is lowered, the concentration or density of the gas or vapor entering is measured as if it is lowered.